Dust concentrator



Dec. 12, 1967 J, WJDRENNING 3,357,159

DUST CONCENTRATOR Filed Sept. 6, 1966 2 Sheets-$heet l PAW/0L: /5

LADE/V CLEAN 6/45 INVENTOR. JOHN W DPENN/NG Dec. 12, 1967 J. w. DRENNING3,357,159

DUST CONCENTRATOR 7 Filed Sept. 6, 1966 2 Sheets-Sheei 1",

/5 55 a E v 1 53 u i n: 5/

INVENTOR.

United States Patent 3,357,159 DUST CUNCENTRATOR John W. Drenning,Baltimore, Md., assignor to Koppers Company, Inc, a corporation ofDelaware Filed Sept. 6, 1966, Ser. No. 577,262 Claims. (Cl. 55-112)ABSTRACT 05 THE DISCLOSURE Electrostatic precipitator apparatus forremoving particles from a gas stream by way of a discharge electrodewhich charges the particles passing by it so that the particles migratetoward a collector electrode is improved by forming the collectorelectrode as two concentric tubes which surround the discharge electrodeand providing means for selectively using one of the tubes as acollecting electrode while previously deposited particles are beingremoved from the other tube.

This invention relates to the separation of solid particles from gaseousstreams.

Separating a particle-laden gas stream into two streams while using anelectrostatic charge to concentrate the particles that are carried in agaseous stream into the one stream which is a minor portion of the totalgas volume and thus removing the particles from the other stream whichis the major portion of the gas volume is described in Lagarias PatentNo. 2,906,369. In such apparatus, the total gas volume is flowed at highvelocity in an ionizing chamber past a discharge electrode where theparticles receive an electrostatic charge and migrate toward a collectorelectrode. The gas stream is divided into the two streams, one of whichis a major portion of the gas volume and the other is a minor portion ofthe gas volume. Due to the particles movement toward the collectorelectrode, the major portion is freed of the particles, and the streamthat is the minor portion of the gas volume flows past the collectorelectrode at such rate as to carry the particles beyond the collectorelectrode. Thus, the burden of particles in this minor portion isincreased and this portion is flowed on to a secondary gas removingapparatus for the cleaning of this stream. Accordingly the particles arenot deposited on the collector electrode as they are in a conventionalelectrostatic precipitator.

Despite the high velocity of the gas and the scouring action due to thehigh velocity of the gas, it has been found that in actual operation, atendency still exists for the particles to accumulate on the collectorsurface. While this tendency is slight, nevertheless the deposition doesdecrease the efiiciency of the unit.

This invention, therefore, is an improvement upon the apparatus ofPatent No. 2,906,369 in the provision for cleaning the collectorelectrode surface. However, the invention is also advantageouslyemployed with gas cleaning apparatus where the velocity of the gas isnot so great as to have unusual scouring action. In this latterapplication, the collected particles are mechanically removed.

In accordance with this invention, the collector electrode is comprisedof two surfaces. When the particles accumutate on a first surface, thisfirst surface with any accumulated particles thereon is removed fromassociation with the discharge electrode and replaced with a secondsurface, meanwhile the first surface is cleaned. In applicationsinvolving gases which are flowing at high velocity, the surfaces arecleaned by being subjected to the scouring action of the high velocitygas. In other applications, the surfaces are mechanically cleaned.Subsequently the first and second surfaces are reversed and the cyclerepeated.

The above and further objects and novel features of the 3,357,159Patented Dec. 12, 1967 invention will appear more fully from thefollowing detailed description when the same is read in connection withthe accompanying drawings. It is to be expressly understood, however,that the drawings are not intended as a definition of the invention butare for the purpose of illustration only.

In the drawings wherein like parts are marked alike:

FIGURE 1 illustrates partially in schematic fashion a section of a unitof an electrostatic precipitator incorporating an embodiment of theinvention;

FIGURE 2 illustrates the apparatus of FIG. 1 in the condition where theparticles which have accumulated on a first surface are removed whileparticles accumulate on a second surface;

FIGURE 3 illustrates the apparatus of FIG. 1 where the particles whichhave accumulated on the second surface are being removed while theparticles are accumulating on the first surface;

FIGURE 4 illustrates partially in schematic fashion another embodimentof an electrostatic precipitator having an embodiment of the inventionincorporated therein; and

FIGURE 5 illustrates a second condition of the embodi ment of theprecipitator of FIG. 4.

Referring now to FIG. 1, the total gas stream A as is described in theaforementioned Patent No. 2,906,369 flows through inlet 9 into agenerally cylindrical ionizing chamber 10. A discharge electrode 11,which is a wire, imparts an electrostatic charge to the particlescarried in the gas stream. These particles then migrate toward thecylindrical collector electrode surface 13. The outer annular portion ofthe gas stream thus becomes richer in particles while the inner annularor core portion of the gas stream is freed of particles.

The gas volume, itself, is divided into two streams by conduits 15 and17. The clean gas stream B, which is relatively free of particles, flowsin conduit 17 and the particle-laden gas stream C flows in conduit 15.The gas stream flows at high velocity and tends to scour the pariclesfrom the collector electrode denoted generally 13. The gas stream C,which is richer or more concentrated as far as the amount of particleswhen compared with the burden of gas stream A, is flowed through conduit15 to a further or secondary particle removing system. (not shown) such,for example, as a cyclone separator. The relatively clean gas in conduit17 may, for example, be

- flowed onto the discharge stack.

While the velocity of the gas tends to keep the collector electrode 13clean nevertheless a layer of particles can build up on this electrodeand decrease the efliciency of the particles removal. In accordance withthis invention, the collector electrode 13 comprises two cylinders 18and 19. These cylinders are movable so the surfaces of these cylindersare movable relative to each other and to the clean gas duct 19, thismovement being accomplished by power means 21 and 23 which may, ofcourse, be the schematically illustrated electric motors and mechanicalconnections 25 and 27. A suitable resilient boot 29 provides a sealbetween duct 15 and the collector electrod arrangement.

As particle-laden gas A flows past electrode 11, an electrostatic orionizing charge is imparted to the particles and the particles migratetowards collector electrode 13. By the time a quantity of gas reachesthe outlet end of ionizing zone 10, a particle rich annular portion ofgas and a clean core of gas have formed. The clean gas then A flowsthrough duct 17 and the concentrated particle-laden The electrodesurface selection is then changed to provide a new collector electrodesurface. Motive means 21 is actuated to render the surface of cylinder18 ineffective as a collector electrode. Thus the cylinder 18, whichformed electrode surface 13, is moved to the position illustrated inFIG. 2, and the surface of cylinder 19 is now rendered effective to actas the collector electrode 13. The surface of cylinder 18, now beingremoved from the presence of discharge electrode 11, is shielded byconduit 17 and not subjected to the electrostatic field which existedwhen it was in the position illustrated in FIG. 1. Accordingly, theparticles which have collected on the surface of cylinder 18 are readilyremoved then by the scouring action of the concentrated particle stream.

After these particles have been removed from the surface of cylinder 18by this scouring action of the concentrated particle-containing gas andother particles from the incoming gas have tended to accumulate on thecollector electrode surface of cylinder 19, motive means 21 is actuatedand the cylinder 18 is again moved to its position as illustrated inFIG. 3 and motive means 23 is actuated so that the cylinder 19 is movedto a position remote from the discharge electrode 11 so that anyparticles which have accumulated on the surface of cylinder 19 areremoved by the scouring action of the concentrated particle-laden gasstream.

Although the particle-laden gas stream, itself, is usually sufficientfor removing any accumulation of particles on the electrode surface whenthe surface is remote from the discharge electrode; this removal may beaided, if desired of course, by mechanical actions such as a rapping ofthe electrode. The cycle of use of the first and second collectorelectrode may be repeated as often and as frequently as desired.

An embodiment of the invention for use with a mechanical arrangement forremoving the particles from the collector electrode is illustrated inFIGS. 4 and 5. This arrangement isparticularly useful where the velocityof the gas flowing into the precipitator is not great enough to generatean effective scouring action. When the velocity is relatively low,particles carried by the gas deposit on the collector electrode. Theparticles are then removed mechanically from the electrode. Asillustrated in FIGS. 4 and 5, the precipitator is comprised generally ofa discharge electrode 11, a collector electrode 13, a particleladen gasduct 15, and a clean gas duct 17 The excitation for the dischargeelectrode may be supplied by a conventional commercially availableexcitation arrangement.

As herein illustrated, the dirty gas duct 15 may be comprised of walls41 and 42. A generally cylindrical duct 43 has one end 45 fastened towall 41 in a suitable manner such, for example, as welding and the end47 attached to a supporting lattice-work 49. Gas flows through opening 9into the air separating chamber of the precipitator.

Concentric with cylinder 43 is another cylinder 51 which is mechanicallysupported within cylinder 43 'by suitable mechanical means denoted as53. It Will be noted that the collector electrode surface 13 of FIG. 4is the inner surface of cylinder 51 and the collector electrode surfaceof FIG. is the inner surface of cylindrical tube 43. The axial movementof cylinder 51 between the positions illustrated in FIGS. 4 and 5 iseffected by conventional motor 55. Both cylinders 43 and 51 are providedwith a rapping means illustrated schematically by rapping motor 61 andmechanical connections 63 and 65 to a respective cylinder 43 and 51.

In the position illustrated in FIG. 4, the particle-laden gas flows pastdischarge electrode 11. The particles in the gas become charged and movetoward collector electrode surface 13. If the flow of gas is relativelyslow, most of the particles will collect upon electrode surface 13.However, these particles which do not collect thereon flow onwardlythrough the opening between duct 17 and cylinder 51- into the dirty airduct 15. This migration of the particles toward the collector electrode13 has left a clean core of gas which then flows through duct 17.

After sufi'icient particles have collected upon cylinder 51 so that theelficiency of the surface is lowered, power means 55 is actuated to movethe cylinder 51 away from the influence of discharge electrode 11 to theposition shown in FIG. 5, at which position the surface of cylinder 51is shielded by the clean air duct 17 Thereafter, the rapping mechanism61 is actuated to mechanically dislodge the particles from the surface.

During the time the precipitator is in the condition shown in FIG. 5,the inner surface of cylinder 43 is operative as the collector electrode13. When the surface of cylinder 43 has operated as collector electrodeand sufficient particles have collected on this surface to cause thesurface to have lost its efiiciency, cylinder 51 is then moved to theposition illustrated in FIG. 4. At this position, the surface ofcylinder 43 is shielded from the discharge electrode 11 and the rappingmechanism 6-1 is actuated to mechanically dislodge the particles fromcylinder 43. These particles at this time would be caught by the outersurface of cylinder 51. However, as the cylinder 51 moves to theposition illustrated in FIG. 5 the fiow of gas past the electrode willremove any particles lying on its outer surface.

One skilled in the art will understand from the foregoing that variouscombinations of mechanical rapping and gas scouring may be employed withthe novel precipitator that sequentially provides clean surfaces for thecollection of particles from a gas.

I claim:

1. An electrostatic precipitator apparatus for removing particles from agaseous stream containing said particles through the action of adischarge electrode and a collector electrode, whereby as said gaseousstream flows past said discharge electrode, said particles are chargedand are diverted radially toward the periphery of the stream whereby theparticle concentration increases in the outer portion of the streamwhile the particle concentration decreases in the inner portion of thestream, the improvement comprising: said collector electrode beingconstituted of first and second cylinders of diifering diametersconcentrically disposed about said discharge electrode, said secondcylinder being disposable within said first cylinder, means forseparating said inner and outer stream portions into independentstreams, and selection means for selectively employing a surface ofsaid, first and second cylinder as said collector electrode.

2. The apparatus of claim 1 wherein said selection means includes meansfor moving said first cylinder to a position remote from said dischargeelectrode so that the surface of said second cylinder becomes acollecting electrode and the particle-laden outer gas stream scours thesurface of said first cylinder to clean collected particles therefrom,and

further means for moving said second cylinder to a position remote fromsaid discharge electrode so that particle-laden outer gas stream scoursthe surface of said second cylinder to clean collected particlestherefrom.

3. The apparatus of claim 2 wherein said selection means moves saidcylinders to a remote position from said discharge electrode by movingsaid cylinders downstream whereby the surface of a cylinder remote fromsaid discharge electrode is shielded from said electrode by saidseparating means.

4-. The apparatus of claim 1 including first cylinder being fixedlypositioned, said second cylinder being mounted within said firstcylinder for axial movement relative thereto, means for moving saidsecond cylinder, and means for rapping said cylinders.

5. The apparatus of claim 1 wherein said means for separating said innerand outer portions of gas into independent strea-ms is a tube coaxialwith said cylinders.

and so positioned as to shield a cylinder surface from said ReferencesCited discharge electrode.

UNITED 1,378,224 5/1921 1,381,719 6/1921 1,444,845 2/1923 2,307,6031/1943 STATES PATENTS Girvin 55-114 X McGee et al. McGee et al. 55-114Penney 55-115 2,867,285 1/1959 Wintermute 55-136 X 2,906,369 9/ 1959Lagarias 55-136 X 3,068,628 12/1962 Balzer et al. 55-100 FOREIGN PATENTS116,325 2/ 1930 Austria.

HARRY B. THORNTON, Primary Examiner. D. TALBERT, Assistant Examiner.

1. AN ELECTROSTATIC PRECIPITATOR APPARATUS FOR REMOVING PARTICLES FROM AGASEOUS STREAM CONTAINING SAID PARTICLES THROUGH THE ACTION OF ADISCHARGE ELECTRODE AND A COLLECTOR ELECTRODE, WHEREBY AS SAID GASEOUSSTREAM FLOWS PAST SAID DISCHARGE ELECTRODE, SAID PARTICLES ARE CHARGEDAND ARE DIVERTED RADIALLY TOWARD THE PERIPHERY OF THE STREAM WHEREBY THEPARTICLE CONCENTRATION INCREASES IN THE OUTER PORTION OF THE STREAMWHILE THE PARTICLE CONCENTRATION DEREASES IN THE INNER PORTION OF THESTREAM, THE IMPROVEMENT COMPRISING: SAID COLLECTOR ELECTRODE BEINGCONSTITUTED OF FIRST AND SECOND CYLINDERS OF DIFFERING DIAMETERSCONCENTRICALLY DISPOSED ABOUT SAID DISCHARGE ELECTRODE, SAID SECONDCYLINDER BEING DISPOSABLE WITHIN SAID FIRST CYLINDER, MEANS FORSEPARATING SAID INNER AND OUTER STREAM PORTIONS INTO INDEPENDENTSTREAMS, AND SELECTION MEANS FOR SELECTIVELY EMPLOYING A SURFACE OF SAIDFIRST AND SECOND CYLINDER AS SAID COLLECTOR ELECTRODE.